1. Field of the Invention
The present invention relates generally to an electronic timepiece having an electro-optical display and, more particularly, to an improved switching arrangement which employs no moving parts for actuating the display.
2. Description of the Prior Art
Electronic timepieces such as electronic wrist watches are well known in the art. A typical electronic timepiece includes a crystal-controlled oscillator circuit for generating a high frequency reference signal, a divider circuit for dividing the high frequency signal into a lower frequency signal, an electro-optical time display such as an array of segmented liquid crystal elements, a display circuit for effecting display of different time intervals, a replaceable battery for powering the electronic components, and a manual switching means for selectively actuating the display circuit. The electronic components are assembled together in a timekeeping module commonly referred to as the watch movement.
The watch movement is mounted within a protective watch case which normally includes a generally tubular side wall, a transparent face cover secured to the upper peripheral edge of the side wall, and a bottom plate secured to the lower peripheral edge of the side wall. The watch movement is placed within the case with the time display means disposed beneath the transparent face cover. The side wall may be provided with a number of openings through which various knobs or push buttons extend to permit manual control of the function displayed by the display means. Some watch movements are designed so that the visual time display means will be illuminated only when the wearer wishes to know the time. In these watches the side wall of the case must be provided with an additional manually operated push button in order to illuminate the time display means.
The presence of several knobs or push buttons protruding from the side wall of a conventional electronic watch detracts from the aesthetically pleasing appearance of the watch case and contributes to the possibility of accidental damage to the vulnerable parts to which they are attached. Furthermore, because the conventional mechanical push-button switch necessarily includes a shaft projecting through the side wall, there is increased potential for water leakage and for wear failure. The presence of the shaft and knobs impose restrictions and limitations on the case styling and case thickness. The conventional mechanical switch is also subject to functional failure due to dirt buildup on its electrode contacts. Such switches are difficult to repair and normally must be returned to the manufacturer for repair at considerable inconvenience and expense to the owner.
A number of approaches have been tried to avoid the problems associated with the conventional mechanical switch. For example, an electronic watch having a magnetic switch is illustrated in U.S. Pat. No. 3,782,102. Magnetic buttons are located inside the watch case to eliminate the case holes, but such arrangements are expensive, space consuming and require a magnetic bar. In another approach, a plastic watch case with a flexible area on the case has been devised to activate switch contacts located inside the case. Such plastic cases have not gained widespread acceptance within the industry. Yet another approach is illustrated in U.S. Pat. No. 3,871,170 which discloses an inertial switch which is responsive to a predetermined movement of the wearer's arm for actuating a display circuit. Switching is accomplished by means of an electrically conductive metal sleeve in which is mounted a free floating electrically conductive metal ball. Such inertial switches are relatively expensive, space consuming, and in some situations are difficult to operate.
The introduction of electronic technology to the field of wrist watches has provided a new set of opportunities and problems. One of the opportunities includes the provision of a large array of new functions such as dual time zones, stop watches, alarms and date reminders in addition to the traditional displays of time, month-date, and seconds. A difficult problem as discussed above is that of making electrical contact to implement these new functions.